1. Field of the Invention
This invention broadly relates to energy absorbing structures, and deals more particularly with energy absorbing elements such as stanchions and assembly fittings used in aircraft.
2. Description of the Related Art
An important objective in the design of modern military and civilian aircraft is the protection of occupants in the event of a survivable crash. Crash injuries may be caused by high acceleration loads experienced by the occupants, or the loss of structural integrity of the aircraft. Crashworthy designs for aircraft require the fuselage to provide energy absorption in order to slow down the aircraft during a crash impact. Controlled deceleration of the aircraft during impact reduces inertial loads on the occupants, and assists in maintaining structural integrity of the aircraft. The area beneath the fuselage floor can form an important part of the energy absorption system in the event of a crash, since this area is normally the part of the aircraft that is initially crushed during ground impact.
Earlier generations of crash energy absorption systems relied heavily on metal components to absorb aircraft kinetic energy during a crash. However, the increasing use of composite materials in aircraft designs has resulted in newer crash energy absorption systems that rely on components formed of composite materials. Energy absorbing systems that use composite materials present a design challenge because these materials are often brittle and do not exhibit either plasticity or high elongation prior to failure. In order to solve these design problems, a number of solutions have been proposed, including varying the density of stitching used in stitched composite structures, and using so called ply drop-offs to sustain a crushing process after it is initiated. These design solutions may sometimes be difficult to incorporate into manufacturing processes without significant cost increases. In addition, previous design solutions were limited to protecting occupants from impact forces acting vertically on the aircraft, rather than from off-vertical forces which can be imposed on the fuselage if the aircraft rolls slightly before ground impact.
Accordingly, there is a need for energy absorbing structure for aircraft that both improves crashworthiness and is cost effective to implement. The invention is directed towards satisfying this need.